FREE CONVECTION INVESTIGATION ON HEAT TRANSFER FROM HORIZONTAL RECTANGULAR AND SQUARE DUCTS.

للكاتب :

Mohamed E. Ali

Mechanical Engineering Department, King Saud University,

ABSTRACT

experimental investigations have been reported on steady state natural convection from the outer surface

of horizontal ducts in air. Five ducts have been used with aspect ratios (Γ= duct height/duct width) of 2, 1

and 0.5. The ducts are heated using internal constant heat flux heating elements. The temperatures along

the surface and peripheral directions of the duct wall are measured. Longitudinal (circumference

averaged) heat transfer coefficients along the side of each duct are obtained for laminar and transition

regimes of natural convection heat transfer. Total overall averaged heat transfer coefficients are also

obtained. Longitudinal (circumference averaged) Nusselt numbers are evaluated and correlated using the

modified Rayleigh numbers for transition regime using the axial distance as a characteristic length.

Furthermore, total overall averaged Nusselt numbers are correlated with the modified Rayleigh numbers,

the aspect ratio and area ratio for the laminar and transition regimes. The longitudinal or total averaged

heat transfer coefficients are observed to decrease in the laminar region and increase in the transition

region. Laminar regimes are obtained only at very small heat fluxes otherwise transitions are observed.

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